Within the disk drive system manufacturing industry, much attention is presently being focused on the performance and reliability of transducers utilized as part of the read/write head. Changes in the operating characteristics of a read transducer, for example, may be indicative of read/write head performance degradation or impending failure of the head. Changes in the amplitude of a readback signal obtained from a particular read/write head, for example, may indicate a possible problem with the read element of that read/write head.
It has been found, for example, that monitoring the amplitude characteristics of a readback signal obtained using a particular read/write head over time may provide insight as to the integrity and operating condition of the read transducer provided on the read/write head. A giant MR (GMR) transducer that is operating in an anomalous manner, by way of example, may produce readback signals of decreasing amplitude over time. The nature and complexity of most read channel designs, however, generally preclude in-situ determination of readback signal characteristics, such as determining, with a high degree of accuracy, readback signal amplitude for a particular read/write head over time.
In a typical read channel design, a variable gain amplifier (VGA) is often employed as the gain element of an automatic gain control (AGC) loop which is used to regulate the amplitude of readback signals provided at the output of the VGA. The AGC loop modifies the gain of the VGA by applying appropriate control signals to the VGA. Although attempts have been made to use VGA control signals for purposes of estimating the amplitude of readback signals input to the VGA, such attempted implementations wholly ignore temperature related factors that adversely affect the accuracy of readback signal amplitude estimates.
There exists a keenly felt need in the disk drive system manufacturing community for an apparatus and method for determining the amplitude of a readback signal obtained from a data storage medium with a high degree of accuracy. There exists a particular need for such an apparatus and method that may be implemented in-situ a read channel. The present invention fulfills these and other needs.